Drives for various forms of discontinuous movement, particularly for pulling and for percussive movements, usually involve pneumatically or hydraulically operated means with driven pistons and with a piston rod transmitting the movement or force to the outside of a cylinder. Linear transporters can operate without a piston rod and the movement work accomplished by the driven piston is coupled to the outside by a longitudinally extending slot provided in a cylinder and, further, there is commonly a force reversal involving a mechanical coupling and a slide. A linear transporter operating without such a piston rod generally has somewhat more than half the overall length of the conventional piston arrangement involving a piston rod and, as a result of the considerably shortened overall length, solves certain arrangement and positioning problems. Although reduced overall lengths can be necessary and important for certain arrangements or for the installation of a drive within an apparatus, and although such arrangements can be achieved with commercially available linear drives of the desired length, it frequently occurs that the force to be used must still be reversed to bring it to the right place.
Instead of constructing the device around the drive or adapting the concept of the device to the physical shape of an available drive, it is theoretically possible to adapt the drive, in this case a linear drive, to the device to be driven. However, it is not always possible to easily reverse the action tasks of systems having relative actions such that, for example, instead of the dentist's drill it is the patient who is rotated. It must be recognized that there are insurmountable factual compulsions which must be respected and preference must be given to long-established experience in this respect.
Such factual constraints are also present in a system having a drive and a driven device and attempts have been made to counteract these by shortening the overall length in the case of the linear drive. Considerable improvement regarding the overall length is provided by the omission of the piston rod. Apart from the "floating piston" of the Sterling motor, this idea which avoids previously existing concepts is not particularly old.
The generation of forces along a general path and the transfer of those forces to an action point would make it possible to nevertheless use such a drive within certain structural limitations in already designed means or in those where drives of the previously mentioned type can be used only with topographical difficulties. Importance must not be attached to the fact that the point at which the force is to ultimately be used is not on the action line of the drive because the path along which the force passes can be brought in virtually any desired way to such a point.